The Pulfrich Effect

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Image: Wikimedia Commons

When you view a pendulum swinging laterally before your eyes, your brain understands correctly that the bob is moving in a straight line perpendicular to your line of sight. But if you put a dark filter over one eye, the bob seems to move in an ellipse, swinging somewhat closer to the screened eye.

Apparently the visual system responds more quickly to bright objects than to dim ones, so when the clear eye correctly sees the bob’s position at A, B, and C, the obscured eye sees it at A’, B’, and C’, and the brain reconciles these reports by supposing it’s at A*, B*, and C*. German physicist Carl Pulfrich first described the effect in 1922.

| Oddities · Science & Math

The Devil’s Golf Course

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Death Valley contains an enormous jagged salt flat produced by the evaporation of an ancient lake.

It takes its name from a 1934 National Park Service guidebook, which declares that “only the devil could play golf on such rough links.”

| Oddities

Neck Deep

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Image: Wikimedia Commons

In 1999, while serving as research fellows at Cambridge University’s Cavendish Laboratory, physicists Thomas Fink and Yong Mao made a mathematical study of necktie knots. They published a summary in Nature that year and a detailed exposition in Physica A in 2000.

They found that, if knots are modeled as persistent random walks on a triangular lattice, there are exactly 85 ways to tie a tie. Of the 10 knots they scored as most aesthetic (for symmetry and balance), only four (four-in-hand, Pratt knot, half-Windsor, Windsor) are well known to Western men; interestingly, the simplest of the remainder, the unassuming small knot, above, is popular in the communist youth organization in China.

Here’s a list of the most aesthetic knots in their list.

| Science & Math

Sliding Dominoes

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Image: Wikimedia Commons

The squares of a 9×9 board are colored as shown, and then its surface is covered with 40 dominoes. Each domino covers two orthogonally adjacent squares, and the uncovered square is a black square on the boundary.

A move shifts a domino along its length by one square, so that it covers one empty square and exposes another. Prove that, for each of the black squares on the board, there’s a sequence of moves that will uncover it.

Click for Answer
| Puzzles

Inspiration

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The creature from the Black Lagoon has the best possible pedigree. As director Jack Arnold was planning the iconic monster’s 1954 debut, his eye fell on his Academy Award nomination certificate for With These Hands, a documentary he’d worked on three years earlier.

“I said, ‘If we put a gilled head on [the Oscar statuette], plus fins and scales, that would look pretty much like the kind of creature we’re trying to get,'” he told Cinefantastique in 1975. “So they made a mold out of rubber, and gradually the costume took shape.”

Former Disney animator Milicent Patrick and makeup artist Bud Westmore collaborated on the creature. “They gave him some human characteristics, which helped to make him sympathetic,” Arnold said. Today the film is regarded as a classic of monster horror — but it didn’t earn an Oscar.

| Entertainment · Trivia

Daring

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We have more respect for a man who robs boldly on the highway, than for a fellow who jumps out of a ditch, and knocks you down behind your back. Courage is a quality so necessary for maintaining virtue, that it is always respected, even when it is associated with vice.

— James Boswell, Life of Samuel Johnson, 1791

| Society

Words and Numbers

Andrzej Bartz offered these “doubly true” alphametics in the May 2017 issue of Word Ways. If the letters in each equation encode digits, what mathematical facts do these expressions represent?

CCCLVI + CCCI + CCLI = CMVIII

ONE + THIRTYNINE + NINETYONE = THREE + NINE + THIRTY + EIGHTYNINE

TWO × TWO + TEN × FIVE = SIX × NINE

Click for Answer
| Puzzles

Hue and Cry

The story goes that one day when Cézanne was picknicking in the country with some friends and a collector, the latter suddenly realized that he had dropped his overcoat somewhere on the way. Cézanne raked the landscape with his gaze, then exclaimed: ‘I’ll swear that black over there doesn’t belong to nature!’ Sure enough, it was the overcoat.

— André Malraux, The Voices of Silence, 1978

| Art

Overboard

1931 saw the publication of a remarkable detective novel. The Floating Admiral had been written by 12 members of the Detection Club, London’s society of mystery writers:

  1. Victor Whitechurch
  2. G.D.H. Cole and Margaret Cole
  3. Henry Wade
  4. Agatha Christie
  5. John Rhode
  6. Milward Kennedy
  7. Dorothy L. Sayers
  8. Ronald Knox
  9. Freeman Wills Crofts
  10. Edgar Jepson
  11. Clemence Dane
  12. Anthony Berkeley

They had written a chapter apiece, serially, without communicating. Each inherited the manuscript from the last and had to make some private sense of the story, including their own complications, before passing it on to the next contributor. To ensure fair play, each writer had to supply a satisfactory solution to the snowballing mystery when they turned in their own chapter.

Amazingly, it worked. Jacques Barzun wrote, “These members of the (London) Detection Club collaborate with skill in a piece of detection rather more tight-knit than one had a right to expect. There is enough to amuse and to stimulate detection; and the Introduction by Dorothy Sayers and supplements by critics and solvers give an insight into the writers’ thoughts and modes of work.”

Here it is.

| Literature